Calling it lack of support is probably a bit misleading, in reality they are actively undermining the competitive scene by things like shutting down tournaments/streams, preventing outside orgs (eg evo, mlg) from picking up smash, etc. Some of the other commenters gave links which have more details on this.

Given the recent events in context of the past 2 decades of nintendo's behaviour, the smash scene would love for nintendo to not be involved at all. There is no entitlement whatsoever for nintendo's support (unless "support" literally just means allowing us to run events with no help of any kind from nintendo other than not shutting it down, in which case it really doesn't strike me as too unreasonable).